Stem load determining system

ABSTRACT

A stem load determining system comprises a method and apparatus for determining the load developed on a threaded stem, including a valve stem driven by a valve operator. An integral component of the apparatus is a stem strain transducer uniquely designed to girp a threaded stem to define a guage length on the threaded stem and to detect and measure deformation of the stem at the guage length when subjected to a compressive or tensile load.

This application is a continuation of application Ser. No. 041,006,filed Apr. 21, 1987, which is a continuation of application Ser. No.036,024, filed Apr. 8, 1987.

FIELD OF THE INVENTION

The present invention relates generally to the field of strain andstress measuring devices and more specifically to devices for themeasuring of strain and stress on thread bearing stems withinflow-controlling valve systems.

BACKGROUND OF THE INVENTION

The ability to measure thrust in a valve operator has becomeincreasingly important since the advent of the Charbonneau et alinvention disclosed in U.S. Pat. No. 4,542,649. More importantly, theneed to measure operator thrust while the operator is attached to thevalve has been identified. Charbonneau and other prior art have utilizedload cells mounted to the upper bearing housing to measure stem load asthe valve stem rises from the close-to-open position to strike themounted load cell. The load cell technique of measuring stem load is notalways functional, since many valve operator designs do not have anupper bearing housing to which a load cell can be mounted.

SUMMARY OF THE INVENTION

Briefly described, the present invention comprises a method, andassociated apparatus, for determining the load developed on a valve stemdriven by a valve operator. The method of the present invention utilizesknown principles and specifications related to stress and strain ofmetals, and specifically threaded shafts; and applies these principlesand specifications in combination with the unique apparatus of thepresent invention. The method and apparatus of the present inventiondetect and measure deformation of the threaded portion of the valve stemwhen the stem is loaded. The measured deformation is recorded andinputed to a calculating device for determination of the load imposed onthe stem. In the preferred embodiment, compressive deformation andcompressive loads are measured and determined; however tensile iscontemplated.

The apparatus of the present invention comprises a unique threadgripping assembly which tightly and rigidly grasps the threaded portionof the valve stem such that the gripping assembly moves with the stem.The gripping assembly includes spaced apart reference points which moverelative to one another, yet are rigidly attached to the threadsdefining a test segment (also referred to as guage length) of thethreaded portion. As the metal body of the valve stem deforms (i.e.compresses or stretches) under load, the reference points move relativeto oneanother. Thus, the deformation of the test segment is mirrored bymovement of the reference points. The relative movement of the referencepoints is detected, measured and recorded by the apparatus of theinvention. The measured deformation is, in preferred embodiments, inputwith other materials specifications to a calculating device in which theload is calculated.

In the preferred embodiment of the present invention, deformation of thetest segment is measured in two locations to compensate for bending ofthe stem under load. Furthermore, the apparatus of the inventioncomprises uniquely shaped, tapered-conical gripping elements which, incombination with clamping members, are instrumental in accomplishing thenecessary grip on the threads of the valve stem, whereby the referencepoints move accurately with deformation of the stem.

It is understood that the method and apparatus of the present inventionand the stem load calculated hereby have broad, cross-industryapplications; and, without limiting such applications, the inventionfinds specific application in the valve diagnostic industry as animprovement to the Charbonneau et al invention of U.S. Pat. No.4,542,649, the disclosure of U.S. Pat. No. 4,542,649 being herebyincorporated herein by reference.

It is, therefore, an object of the present invention to provide a methodfor determining load on an operator driven valve stem as the valve stemmoves from the open to close position.

Another object of the present invention is to provide a method andapparatus for determining valve stem load by mounting measuring deviceson the threaded portion of the valve stem.

Yet another object of the present invention is to provide a method andapparatus for measuring deformation of a valve stem subjected to a load.

Still another object of the present invention is to provide apparatusfor rigidly gripping screw threads and detecting deformation of thethread shaft upon loading.

Other objects features and advantages of the present invention willbecome apparent upon reading and understanding this specification, takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of stem load determining system in accordancewith the present invention, as used in conjunction with a valve andvalve operator.

FIG. 2 is an isolated side view of the stem strain transducer of thestem load determining system of FIG. 1.

FIG. 3 is a top view of FIG. 2.

FIG. 4a is a side view of a stud member in accordance with the presentinvention.

FIG. 4b is an end view of the stud member of FIG. 4a.

FIG. 5 is a schematic representation of the electronic devices of thestem load determining system of FIG. 1.

FIG. 6 is an isolated view of a thread portion showing engagement of astud member in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in greater detail to the drawings in which like numeralsrepresent like components throughout the several views, FIG. 1 shows (inpartial schematic form) the apparatus of the present invention in itspreferred operating environment. A process pipe 12 is provided with avalve 3, shown as a gate valve. The valve 13 is moved up and down,perpendicular to the fluid flow in the pipe 12, by a valve stem 15. Thevalve stem 15 is driven up and down by a gearing device 16, known as avalve operator 16. The operator 16 is supported above the valve 13 by ayoke 17. In the preferred embodiments, the operator is manually operatedby a handwheel 18 or motor operated by a motor 19.

As seen in FIG. 1, a stem strain transducer 24 is mounted on thethreaded portion 20 of the valve stem 15. Detailed in FIGS. 2 and 3, thestem strain transducer 24 comprises a left clamp half 25 and a rightclamp half 26. The left clamp half 25 includes a support plate 28 towhich is rigidly attached an upper gripping plate 29 and a mountingbracket 30. A lower gripping plate 31 is releasably attached, as bybolts 35, to the support plate 28. A linear variable differentialtransducer ("LVDT") 32 is attached to the bracket 30 and the stylus(core extension) 33 of the LVDT contacts the top surface 34 of the lowergripping plate 31. The right clamp half 26 includes a support plate 38to which is rigidly attached an upper gripping plate 39 and a mountingbracket 40. A lower gripping plate 41 is releasably attached, as bybolts 45, to the support plate 38. An LVDT 42 is attached to the bracket40 and the stylus (core extension) 43 of the LVDT contacts the topsurface 44 of the lower gripping plate 41. The LVDTs are of a typetypical in the industry having a core moving through a stationary baseto effect a voltage output signal.

FIG. 3 is a top view of the assembly of FIG. 2, and only the two upperplates 29, 39 are in view. However, the lower plates 31, 41 are similarin construction and assembly. Each of the four gripping plates 29, 31,39, 41 is formed with a wedge-shaped concavity 50 defining its frontedge 50, and a back edge 51 by which the gripping plate is attached tothe respective support plate 28, 38. The ends 52, 53 are formed withbolt channnels 54, 55. Two stud accepting bores 58, 59 are drilled intothe front edge of each gripping plate 29, 31, 39, 41, each bore beingoriented with its centerline 62 perpendicular to one side of the wedgeof the front edge. Access is had to each bore 58, 59 from the back edge51 of the plate 29, 31, 39, 41 by a screw channel 60, 61. A stud member63, 64 is held in each bore 58, 59 by a screw through the screw channel60, 61. The stud member 63, 64 is adjustable for rotational and axialmovement within the bore 58, 59. Each stud member 63, 64 is uniquelyformed with a cylindrical body 65 and a tapered-conical head 66, as seenin greater detail in FIGS. 4a and 4b. In the preferred embodiment, thecone of the head 66 defines an angle "a" in profile of about 90'. Thecenterline 68 of the conical head 66 is offset from the centerline 69 ofthe body 65. In the preferred embodiment, the head center-line 68 isoffset a distance equal to about one-half of the radius of the stud body65. FIG. 4a also indicates the threaded channel 71 by which a screwholds the stud member 63, 64 in the bore 58, 59. A key hole 72 isdrilled in the stud member 63, 64 toward the head end.

With reference now to FIGS. 1 and 5, the electronics portion of theapparatus of the present invention is seen as including a power supply74 supplying power to a conditioning device 75. The conditioning device74 includes a conditioning module 77, 78 for each of the LVDTs 32, 42.Each conditioning module 77, 78 provides excitation power to itsrespective LVDT 32, 42 and receives the LVDT signal, along wiring 79,80. In the preferred embodiment, the modules 77, 78 provide demodulationand amplification of the LVDT signal, and convert the LVDT output into afiltered, high level DC signal. Such modules are available "off-theshelf". The conditioning device 75 further includes a summing module 81which combines the output signals from the two conditioning modules 77,78 into a single output from the conditioning device. The summing deviceincludes an amplifier 82, separate input resistors R1 and R2, a feedbackloop 83 (including resistors R3 and R4), and bias-current compensatingresistor R5. The values of the resistors are varied by choice to providea desired output. For example, the output from the summing module 81 inone embodiment is an average of the two signals from the conditioningmodules 77, 78 (in such case, the resistor values are R1=R2=10 Kohms,R3=4.5 Kohms, R4=1 Kohms, the R3-R4 pair being adjustable to 5 Kohms,R5=2.5 Kohms); but, in another embodiment, the summing module output isthe sum of the two conditioning module signals (R1=R2=10 K; R3=9.5 K,R4=1 K adjustable, R5=4.3 K). The respective outputs are, typically, inthe form of DC voltages.

The output signal from the conditioning device 75 is delivered alongcable 85 to a recording device 86, such as an osciloscope, at whichdevice the signal values are recorded and where such signal values canbe visually observed. The voltage signal from the conditioning device 75is related to a corresponding distance measurement value at therecording device 86. From the recording device 86, the distance valuesare transferred to a computing device 87, either electronically as bycable 88 to a computer, or manually as by keypad to a calculator.

OPERATION

The above described apparatus is connected to the valve stem 15 throughthe mounted stem strain transducer 24. In practice, it is best to drawthe valve 13 partially open and out of its seat, such that the valvestem is in a relaxed state (that is, experiencing no compressivestress). The stem strain transducer 24 is then mounted to the threadedportion 20 of the valve stem 15 near the top of the yoke 17. In thismanner, as the valve 13 is again closed, the strain transducer will notbind against the top of the valve housing 14. Prior to mounting of thestem strain transducer 54 on the valve stem 15, the clamp halves 25, 26are assembled per the above description. The lower gripping plates 31,41 are bolted against movement to the respective support plates 28, 38.Note that the top surfaces 34, 44 of the lower gripping plates 31, 41,when attached to the support plate 28, 38 are spaced apart from the LVDTmounting brackets 30, 40. Mounting of the transducer 24 is accomplished,with reference to FIG. 2, by aligning the two clamp halves 25, 26 at thethreaded portion 20 of the valve stem 15, with one clamp half 25, 26 oneach side of the axial plane 90 of the valve stem 15. As seen in FIG. 3,the wedge-shaped concavities 50 of the various gripping plates 29, 31,39, 41 cradle the stem 15. The stud members 63, 64 of all of thegripping plates 29, 31, 39, 41 are drawn tightly into their respectivestud accepting bores 58, 59 by a screw within the screw channel 60, 61.As the clamp halves 25, 26 are aligned on the threaded portion 20, thetapered-conical heads 66 of the various stud members 63, 64 project intothe valleys 91 of the stem threads--each head 66 projects into onevalley (see FIG. 6). The cone shape of the head 66 assists in a snug fitof the stud member 63 on threads of varying size. The offset nature ofthe tip 67 assists in compensating for the pitch and lead of the subjectthreads in order to maintain the paired, upper plates 29, 39 and thepaired, lower gripping plates 31, 41 in parallel alignment. Thetapered-conical heads 66 of the various stud members are rotated aboutthe body centerlines 69 to assure a good fit within the thread valleys91, and provide for approximate, parallel alignment of the pairedgripping plate. In the preferred embodiment, once the two clamp halves25, 26 are mounted in alignment on the stem 15, the body centerlines 69of the four stud members 63, 64 in the two upper gripping plates 29, 39all lie within a single plane, perpendicular to the axial plane 90 ofthe valve stem; and the body centerlines 69 of the four stud members 63,64 in the two lower gripping plates 31, 41 all lie within a singleplane, pependicular to the axial plane 90. Preferrably, the centerlines68 of the various stud heads 66 are as close as practicable to therespective planes of the body centerline 69. Rotating of the studmembers 63, 64 about the body centerline 69 is aided by inserting of apin into the keyholes 72 and using such pin as a lever. The stud members63, 64 are tightened within the bores 58, 59 by the screws in screwchannels 60, 61 to hinder further movement. The paired gripping plates29, 39 and 31, 41 are drawn together about the stem 15 by bolts 56, 57through the bolt channels 54, 55.

The head centerlines 68 of the stud members 63, 64 function as referencepoints, marking reference points on the stem 15. The reference pointsdefine a test segment or guage length ("L") on the valve stem 15. Theaxial distance between corresponding reference points (head centerlines)67 of the gripping plates 29, 31, 39, 41 ae measured. Thus, measure thedistance between head centerlines 68 of stud members 63 of left halfgripping plates 29, 31; the distance between head centerlines 68 of studmembers 64 or left half gripping plates 29, 31; the distance betweenhead centerlines 68 of stud members 63 of right half gripping plates 39,41; and the distance between head centerlines 68 of stud members 64 ofright half gripping plates 39, 41. The average of these four distancesis taken as the guage length "L" and is entered into the memory of thecomputing device 87. The LVDTs 32, 42 are connected to the conditioningdevice 75 which is connected to the recording device 86, as disclosedabove. In the preferred embodiment, each LDVT 32, 42 is mounted to itsrespective clamp half 25, 26 in such a manner that, when the clamphalves are mounted to the valve stem 15, the cores (style 33, 43) of theLVDT's 32, 42 are spaces apart 180° radially about the centerline of thevalve stem and equidistant from the centerline of the stem. At thistime, the bolts 35, 45 which hold the lower gripping plates 31, 41 totheir respective support plate 28, 38 are removed such that the lowergripping plates 31, 41 are now clamped by bolts, 56, 57 to the valvestem 15 but are free to move relative to the LVDT mounting brackets 30,40.

The valve stem 16 is now driven downward by either manual or motoroperation of the valve operator 16, to close the valve 13. As the valve13 seats in the closed position a compressive load (the "stem load") isdeveloped with the valve stem. The stem load continues to increase untilsuch time as the torque switches within the valve operator trip todisengage the operator (or manual operation is stopped).

The compressive load to which the stem 15 is subjected results in acompression of the deformable material of which the stem is made. As thestem 15 is compressed, the test segment (guage length) of the stem,which is defined by the distance "L", is proportionately compressed. Asthe test segment is compressed, the lower gripping plates 31, 41 moverelative to the LDVT mounting brackets 30, 40. The reference surfaces34, 44 move the LDVT stylus 33, 43 which creates a relative movementbetween LDVT core and base (as known in the industry) to generate asignal representing the change ("dL") in the length ("L") of the testsection. It can be seen that if the test segment is subjected tobending, the distance between reference points of one clamp half willincrease, while the distance between reference points of the other clamphalf will decrease. The respective LVDT 32, 42 will detect and signal adL indicating the relative increase or decrease. As explained above, thesignal from each LVDT 32, 42 is passed from the respective conditioningmodules 77, 78 to the summing device 81 where the real values are added,averaged, or otherwise conditioned, and then sent to the recordingdevice 86 where the conditioned signal is displayed or otherwiserecorded. In the preferred embodiments, a time related trace of thechange (dL) in test length "L" is recorded and displayed. A sample ofsuch trace 93 is seen in FIG. 5. The distance value recorded at therecording device 86 is next entered into the computing device asdiscussed above. It is understood that the recording and computing stepsare combinable.

The final determination of an actual value of the stem load is based onprinciples of strength of materials and elastic bodies. The followingformulas are known in the art and are appropriate:

    Strain=dL

    Stress=(strain)×(modulus of elasticity)

    Force=(stress)×(stress area)

Stress Area for a thread section is based on the mean of the minimumpitch diameter (P) and the minimum minor diameter (K), thus:

    Stress Area=π (P+K)/4!.sup.2

Therefore, the following calculation is accomplished by the computingdevice 87:

    F=π dL E/L!× (P+K)/4!.sup.2

Where:

F is stem load.

dL is as determined by the conditioning device 75. If the summing device81 generates an output which is different than the average dL, theappropriate modification must be made to the above formula.

E is the modulus of elasticity of the stem material.

L is the length of the stem, test segment as previously measured.

P is the minimum pitch diameter of the threaded portion 20 based on thethreads geometry.

K is the minimum minor diameter of the threaded portion 20, based on thethreads geometry.

Whereas, the stem strain transducer 24 is disclosed herein as part of alarger invented system, it is understood that the stem strain transduceris itself unique and finds application in other threaded stemenvironments.

Whereas, the preferred embodiment expressed herein discloses use of anLVDT to detect and measure relative movement between two referencepoints, it is within the scope of the present invention to use othermovement detecting devices to accomplish the similar goal.

Whereas, the preferred embodiment of the present invention discloses useof the stem strain transducer 24 to define a test segment and to trackreference points defining the limits of the test segment, it is withinthe scope of the present invention to utilize other methods toaccomplish the same goal, within the more expansive apparatus and methodof the present invention.

Whereas, the present invention is described in detail with specificreference to preferred embodiments thereof, it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described before and as defined in the appendedclaims.

We claim: . .1. An apparatus for monitoring the axial deformation in astem or other symmetrical object which is subjected to a load, saidapparatus comprising: forces..!.2. . .Apparatus of claim 1,.!. .Iadd.Anapparatus for monitoring the axial deformation in a stem or othersymmetrical object which is subjected to a load, said apparatuscomprising:first gripping member positioned along the object; secondgripping member cooperating with said first gripping member toreleasably and tightly grip the object between them; third grippingmember positioned along the object at a position axially displaced fromsaid first gripping member; fourth gripping member cooperating with saidthird gripping member to releasably and tightly grip the object betweenthem; wherein said first and third gripping members are capable ofrelative movement to one another in each of the axial, radial andangular directions in response to forces acting on the object, andwherein said second and fourth gripping members are capable ofindependent relative movement relative to one another in each of theaxial, radial and angular directions in response to forces acting on theobject; first movement detecting means for detecting the axial componentof the relative movement between said first and third gripping membersand for generating an electrical signal representative of said axialcomponent .Iaddend.wherein said first movement detecting meanscomprises, at least:a first striking surface mounted to said firstgripping member. .;.!..Iadd., .Iaddend.and a first LVDT comprising abase element mounted to said third gripping member and a core elementsupported by and protruding from said base element, said core elementbeing movable relative .Iadd.to .Iaddend.the LVDT base element inresponse to relative axial movement between said first and thirdgripping members to generate said electrical signal representative ofsaid axial component of the relative movement between said first andthird gripping members. .;.!..Iadd., .Iaddend. said LVDT core elementcontacting said first striking surface in a manner so as to moverelative to said first striking surface in response to radial andangular deformation of the object and to move with said first strikingsurface in response to axial deformation of the object; . .and.!..Iadd.second movement detecting means for detecting the axial componentof the relative movement between said second and fourth gripping membersand for generating an electrical signal representative of said axialcomponent of movement between said second and fourth gripping members.Iaddend.wherein said second movement detecting means comprises, atleast:a second striking surface mounted to said second gripping member..;.!..Iadd., .Iaddend.and a second LVDT comprising a base elementmounted to said fourth gripping member and a core element supported byand protruding from said base element, said core element being movablerelative to the base element of said second LVDT in response to relativeaxial movement between said second and fourth gripping members togenerate said electrical signal representative of said axial componentof the relative movement between said second and fourth grippingmembers. .;.!..Iadd., .Iaddend. said LVDT core element of said secondLVDT contacting said second striking surface in a manner so as to moverelative to said second striking surface in response to radial andangular deformation of the object and to move with said second strikingsurface in response to axial deformation of the object.Iadd.; means forcombining said signal from first movement detecting means and saidsignal from said second movement detecting means in a predeterminedmanner, thus providing a signal representative of the axial deformationof the object; and said first movement detecting means and said secondmovement detecting means each being so comprised as to not inhibit saidindependent relative movement of said gripping members in each of theradial and angular directions, whereby freedom of movement is availablebetween the first and third gripping members and between the second andfourth gripping members for at least some distance in each of the axial,radial and angular directions and whereby axial deformation of theobject is measurable while the object is experiencing any and all ofaxial, bending and torsional forces..Iaddend.3. Apparatus of claim 2,wherein said core element of said first LVDT contacts said firststriking surface at a location which is displaced 180 degrees about thecenterline of the object from the location at which said core element ofsaid second LVDT contacts said second striking surface, and wherein saidcontact locations are spaced equidistant from the centerline of theobject.
 4. Apparatus of claim . .1.!. .Iadd.2.Iaddend., furthercomprising interconnect means interconnecting said first and secondgripping members for drawing said first and second gripping memberstoward oneanother and tightly against said object; and secondinterconnect means interconnecting said third and fourth grippingmembers for drawing said first and second gripping members towardoneanother and tightly against said shaft. . .5. Apparatus of claim 1,wherein said first movement detecting means comprises, at least:a strikeelement mounted to said first gripping member and movable with saidfirst gripping member; a contact assembly supported by said thirdgripping member, at least a reactive portion of said contact assemblybeing positioned for engagement by said strike element and being movablerelative to said third gripping member within an axial plane parallel tothe axis of the object in response to axial movement of said strikeelement; and signal means responsive to the relative movement betweensaid reactive portion and said third gripping member for generating anelectrical signal representative of the axial component of said relativemovement between said reactive portion and said third gripping member,wherein relative movement between said first and third gripping memberseffects movement of said reactive portion in response to movement ofsaid strike element, which in turn effects generation of said electricalsignal; andwherein said second movement detecting means comprises, atleast: a strike element mounted to said second gripping member andmovable with said second gripping member; a contact assembly supportedby said fourth gripping member, at least a reactive portion of saidcontact assembly being positioned for engagement by said strike elementand being movable relative to said fourth gripping member within anaxial plane parallel to the axis of the object in response to axialmovement of said strike element; and signal means responsive to therelative movement between said reactive portion and said fourth grippingmember for generating an electrical signal representative of the axialcomponent of said relative movement between said reactive portion andsaid fourth gripping member, wherein relative movement between saidsecond and fourth gripping members effects movement of said reactiveportion in response to movement of said strike element, which in turneffects generation of said electrical signal..!.6. . .Apparatus of claim5,.!. .Iadd.An apparatus for monitoring the axial deformation in a stemor other symmetrical object which is subjected to a load, said apparatuscomprising:first gripping member positioned along the object; secondgripping member cooperating with said first gripping member toreleasably and tightly grip the object between them; third grippingmember positioned along the object at a position axially displaces fromsaid first gripping member; fourth gripping member cooperating with saidthird gripping member to releasably and tightly grip the object betweenthem; wherein said first and third gripping members are capable ofrelative movement to one another in each of the axial, radial andangular directions in response to forces acting on the object, andwherein said second and fourth gripping members are capable ofindependent relative movement relative to one another in each of theaxial, radial and angular directions in response to forces acting on theobject; first movement detecting means for detecting the axial componentof the relative movement between said first and third gripping membersand for generating an electrical signal representative of said axialcomponent wherein said first movement detecting means comprises, atleast:a strike element mounted to said first gripping member and movablewith said first gripping member, a contact assembly supported by saidthird gripping member, at least a reactive portion of said contactassembly being positioned for engagement by said strike element andbeing movable relative to said third gripping member within an axialplane parallel to the axis of the object in response to axial movementof said strike element, and signal means responsive to the relativemovement between said reactive portion and said third gripping memberfor generating an electrical signal representative of the axialcomponent of said relative movement between said reactive portion andsaid third gripping member, wherein relative movement between said firstand third gripping members effects movement of said reactive portion inresponse to movement of said strike element which in turn effectsgeneration of said electrical signal; second movement detecting meansfor detecting the axial component of the relative movement between saidsecond and fourth gripping members and for generating an electricalsignal representative of said axial component of movement between saidsecond and fourth gripping members wherein said second movementdetecting means comprises, at least:a strike element mounted to saidsecond gripping member and movable with said second gripping member, acontact assembly supported by said fourth gripping member, at least areactive portion of said contact assembly being positioned forengagement by said strike element and being movable relative to saidfourth gripping member within an axial plane parallel to the axis of theobject in response to axial movement of said strike element, and signalmeans responsive to the relative movement between said reactive portionand said fourth gripping member for generating an electrical signalrepresentative of the axial component of said relative movement betweensaid reactive portion and said fourth gripping member, wherein relativemovement between said second and fourth gripping members effectsmovement of said reactive portion in response to movement of said strikeelement, which in turn effects generation of said electrical signal;means for combining said signal from first movement detecting means andsaid signal from said second movement detecting means in a predeterminedmanner, thus providing a signal representative of the axial deformationof the object; said first movement detecting means and said secondmovement detecting means each being so comprised as to not inhibit saidindependent relative movement of said gripping members in each of theradial and angular directions, whereby freedom of movement is availablebetween the first and third gripping members and between the second andfourth gripping members for at least some distance in each of the axial,radial and angular directions and whereby axial deformation of theobject is measurable while the object is experiencing any and all ofaxial, bending and torsional forces; and.Iaddend. wherein each saidreactive portion is substantially non-responsive to angular movement ofthe respective said strike element about the object axis.